Process of forming free-flowing, particulate mixtures of phosphates and silicates

ABSTRACT

Free-flowing, fast-dissolving, completely soluble, strong, granular particles containing a mixture of a hydratable alkali metal phosphate and an alkali metal silicate wherein the SiO2 to said phosphate mole ratio is at least 1:1, were produced by maintaining the alkali metal phosphate at a temperature of 60* to 100* C., gradually adding an aqueous solution of alkali metal silicate to the alkali metal phosphate, continually evaporating water from the resulting mixture, controlling the rate of addition of the alkali metal silicate solution so that the resulting mixture is maintained in the form of discrete particles, continuing said alkali metal silicate addition until the discrete, granular particles have an SiO2 to said phosphate mole ratio of at least 1:1, and recovering dry-appearing, granular particles which yield a pH of at least 10.5 in an aqueous 1 percent solution.

iiriited States Patent [72] Inventors [22] Filed Apr. 24, 11968 [45] Patented Nov. 116, 19711 [73] Assignee i MC Corporation New York, NY.

[54] PROCESS OF FORMING FREE-FLOWING,

PAlR'llllCULATE MIXTURES 01F PHOSPMATES AND SilLllCA'iiES 8 Claims, No Drawings [52] U.S. Cl 252/385, 23/106, 252/99, 252/109, 252/135, 252/387 [51] llnt.Cl ..Cl]1d17/06 C1 1d 9/14 [50] ll ieid of Search 252/385,

[ 5 6] References Cited UNITED STATES PATENTS 2,909,490 10/1959 Metziger 23/106 3,390,093 6/1968 lFeierstein etal.

Primary Examiner-Richard D. Lovering Assistant Examiner-Irwin Gluck AttorneysEugene G. Seems, Frank lanno and Milton Zucker ABSTRACT: Freeflowing, fast-dissolving, completely soluble, strong, granuiar particles containing a mixture of a hydratable alkali metal phosphate and an alkali metal silicate wherein the Si0 to said phosphate mole ratio is at least 1:1, were produced by maintaining the alkali metal phosphate at a temperature of 60 to 100 C., gradually adding an aqueous solution of alkali metal silicate to the alkali metal phosphate, continually evaporating water from the resulting mixture, controlling the rate of addition of the alkali metal silicate solution so that the resulting mixture is maintained in the form of discrete particles, continuing said alkali :metal silicate addition until the discrete, granular particles have an Si0 to said phosphate mole ratio of at least 1:1, and recovering dry-appearing, granular particles which yield a pH of at least 10.5 in an aqueous 1 percent solution.

PROCESS OF FORMING FREE-FLOWING, PARTICULA'JIIE MIXTURES OF lPllIOSlPllilATlES AND SllLllCATlES BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to producing free-flowing, strong, discrete, granular particles that contain a mixture of a hydratable phosphate and a silicate, and which dissolve rapidly and completely in water.

2. Description of the Prior Art In the process of manufacturing a dry-mixed, built, detergent formulation for use in dishwashers or cleansing, it is common to use a sodium phosphate, e.g., sodium tripolyphosphate, as the builder, along with other common ingredients; these may include anionic or nonionic synthetic surfactants, antiredeposition agents, such as sodium carboxymethylcellulose, extenders, perfumes, bleaching agents, e.g., chlorinated cyanurates, alkaline cleansers, e.g., soda ash, caustic soda, and the like. The above phosphate built detergent, when used in conventional dishwashers or cleansing equipment, is known to be corrosive to both the metal and enamelware it contacts. To inhibit such corrosion, an alkali metal silicate, normally sodium silicate, is incorporated into the detergent formulation. The added alkali metal silicate also increases the alkali content of the detergent formulation, thereby improving detergency and buffering it against acid soils removed during cleansing.

Regrettably, mixing the sodium tripolyphosphate and a silicate in a dry-mixed, detergent formulation results in serious problems. These ingredients tend to combine together into agglomerates that cake and prevent the mixture from being uniform and free flowing. Also, these agglomerates segregate in the detergent package and are not dispersed homogeneously with the remaining ingredients of the detergent formulation. Another serious difficulty is that the highly alkaline, alkali metal silicate particles irritate human skin if these particles contact the hands of the consumer during cleansing or while dispensing the detergent formulation in a dishwasher.

One solution to these problems is set forth in US. Pat. No. 2,909,490, issued to Max Metziger on Oct. 20, 1959. The patent describes the manufacture of duplex compositions of sodium tripolyphosphate and aqueous sodium silicate mixtures by contacting these ingredients at below 60 C. so that anhydrous sodium tripolyphosphate dehydrates the aqueous mixtures of sodium silicate to yield a dry-appearin g mixture.

This patented duplex mixture has certain drawbacks. Initially, it can only be formed with the less alkaline silicates, i.e., SiO /Na O weight ratios of 3.22:] to 2.40:1. Further, when high silica to phosphate mole ratios, e.g., at least 1:1, are desired in the mixture for optimum corrosion inhibition, only the less alkaline (SiO /Na O of 3.22:1) silicates can be employed to obtain the patentees duplex product. This is a disadvantage because higher alkaline ingredients, preferably those yielding products having a pH of at least 10.5 (when made up in an aqueous 1 percent solution thereof), are desired to obtain better detergency and to avoid precipitates in the dissolved detergent formulation. Also, on storage, the high free moisture content of the duplex mixture facilitates lumping and undesired absorption of atmospheric carbon dioxide which converts silicates to insoluble silica and causes clouding of the final detergent solution.

OBJECTS OF THE INVENTION It is an object of the present invention to produce free-flowing, fast-dissolving, completely soluble, strong, granular particles that contain a mixture of a silicate and a hydratable alkali metal phosphate in which the silicate to said phosphate mole ratio is at least 1:1, and the particles yield a pH of at least 10.5 in an aqueous 1 percent solution.

It is a further object of the present invention to produce free-flowing, fast-dissolving, completely soluble, strong, granular particles that contain a mixture of a sodium silicate and a hydratable sodium phosphate in which the sodium silicate has an SiO /Na O weight ratio of below about 2.40: 1.

These and other objects will be apparent from the following description of the invention.

SUMMARY OF THE INVENTION We have now found that free-flowing, strong, granular particles containing a mixture of a hydratable alkali metal phosphate and an alkali metal silicate, wherein the SiO, to said phosphate mole ratio is at least 1:1, can be produced by heating the alkali metal phosphate to a temperature of 60 to 100 C. (preferably 60-75 C.), gradually adding an aqueous solution of an alkali metal silicate (preferably a sodium silicate having an SiO,/Na O weight ratio of below 2411) to the alkali metal phosphate while said alkali metal phosphate is being agitated, maintaining the mixture of said alkali metal phosphate and the silicate at a temperature of 60 to 100 C., continually evaporating water from the resulting mixture, controlling the rate of addition of the silicate solution so that the resulting mixture is maintained in a particulate, dry-appearin g, granular form, continuing to add the silicate solution until the dry-appearing, granular particles have an SiO to said phosphate mole ratio of at least 1:1 and recovering granular particles which yield a pH of at least 10.5 in an aqueous 1 percent solution.

DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS In carrying out the present invention, a hydratable alkali metal phosphate, either in a granular form (-10 to +200 mesh) or powdered form (-100 mesh) is used as one of the feed reactants. The granular form is preferred, particularly in a predominantly -20 +100 mesh size range. The hydratable phosphate may be either sodium tripolyphosphate, u r o tetrasodium pyrophosphate, Nla P O trisodium orthophosphate, Na PO sodium trimetaphosphate, (NaPO or the corresponding potassium salts, namely, potassium tetrametaphosphate, (KPO L, or potassium pyrophosphate, K P O The preferred embodiment is sodium tripolyphosphate which is most popularly used in detergent mixes. When using a hydratable phosphate, e.g., sodium tripolyphosphate, as the feed reactant, it is placed in an agitated reaction chamber such as a Hobart mixer, rotary drum or other agitated vessel, heated to a temperature of 60 to 100 C. (preferably 60to 75 C.), and maintained in a state of constant agitation.

To this agitated, heated bed of hydratable phosphate is then added an alkali metal silicate, preferably a potassium or sodium silicate solution having an SiO /M O weight ratio of below 2.40:1, wherein M is either sodium or potassium. An especially useful sodium silicate solution is the Philadelphia Quartz Company product D-brand silicate which contains 14.7 percent Na O; 29.4 percent SiO and 55.9 percent H O. The silicate solution is dispersed onto the heated bed of hydratable phosphate, preferably through spray nozzles or other line distributing means at a rate that does not cause the resulting mixture to become excessively sticky. Water is constantly evaporated from the resulting mixture to prevent the incoming alkali metal silicate solution from causing the discrete particles of the mixture to adhere into undesirably large aggregates. When the alkali metal silicate solution is added in the proper manner, the resulting mixture remains dry-appearing without changing its granular form and without losing its discrete, particulate character. A major portion of the granular product that is recovered is in the desired l0 mesh range when starting with the preferred -20 mesh, granular, hydratable phosphate. If a finer hydratable phosphate feed is used, i.e., a powdered phosphate, the resulting product will contain some undersized particles, that is, smaller than 80 mesh.

The process can be carried out either in batch form or on a continuous basis. In continuous operation, any undersized particles are recycled back to the agitated bed of hydratable phosphate to be further processed until it is of suitable product size. Oversize particles, if any, can be crushed so that the desired product size, l +80 mesh, is separated, and any undersized fraction is recycled to the agitated, hydratable phosphate bed for further processing.

A sodium silicate solution such as the D-brand silicate which contains about 55 percent water can be used as received from the manufacturer and added directly to the sodium tripolyphosphate. However, in cases where the silicate solution is so viscous that pumping, spraying and/or dispersing of the solution onto the phosphate bed is impeded, sufficient water may be added to the silicate solution to reduce the viscosity of the solution to a suitable, workable level. In addition to reducing the viscosity, the added water permits the silicate solution to be more readily dispersed throughout the bed of hydratable phosphate. However, the addition of excessive amounts of water is undesirable because this water must be evaporated from the mixture and increases the reaction time and heat input required to prepare the final product.

In the manufacture of the preferred product, it is desired to maintain the Si0 to sodium tripolyphosphate mole ratio at a level of at least 1:1 in order to provide good corrosion inhibition. This and higher mole ratios of silicate to sodium tripolyphosphate are sufficient to materially reduce or eliminate undue corrosion of metal equipment that contacts the present silicate-phosphate product when it is incorporated in a final detergent formulation. Examples of some sodium silicate solutions which have been found effective in the present invention are listed below:

The above products are registered trademarks of Philadelphia Quartz Co., Philadelphia, Pa.

The following examples are given to illustrate the present invention and are not deemed to be limiting thereof.

EXAMPLE 1 dropwise at a rate of about 0.2 gram/minute. Water was continuously evaporated from the mixture during the run. The rate of addition of the silicate solution was controlled by observing the mixture; if the discrete particles of the mixture commenced to adhere into undesirably large aggregates, the

addition of the silicate solution was suspended until enough water was evaporated from the mixture to restore its dry-appearing form. The final products were dry-appearing, freeflowing, fast-dissolving, completely soluble, strong particles containing sodium silicate and sodium phosphate; the particles were analyzed, and the results are set forth in table 11. The

physical properties of the particles are also reported in table 11.

The above technique was repeated in other runs using various sodium phosphates and sodium silicate mixtures in different $10, to phosphate mole ratios. The feed materials and their properties are reported in table I, while the properties and analysis of the products are set forth in table 11.

EXAMPLE 2 The procedure of example 1, run 1, was repeated, except that Kasil 88," a proprietary product containing 9.1 weight percent K 0, 19.9 weight percent SiO and 71 weight percent H O was used in place of the sodium silicate solution. The

granular product obtained was found to have the same desirable characteristics of strength, free-flowability and rapid dissolution as the product of run 1.

TABLE I Sodium phosphate properties Sodium silicate solution Mole ratio Bulk Wt. Wt. Wt. 5101/ Run density, percent percent percent Wt. ratio phosphate N 0. Manufacturing method g./ec. Mesh size Name Na o 810; H O slog/N820 in mixture 1 Spray-dried granular SIPP 0.48 All 20 +100 D 14. 7 20. 4 55. 9 2. 00:1 2. 20:1

light-density. 2 Heavy-density rotary kiln 0.90 do D 14. 7 29.4 55.0 2. 00:1 2.20:1

granular STPP. 3 Spray-dried granular STPP 0.47 do D 14.7 29.4 55.9 2. 00:1 2. 20:1

light-density. 4 STPP powder 0. 76 Substantially all 100 D 14. 7 29. 4 55. 9 2. 00:1 2. 20:1 5 Spray-dried granular SIPP 0.48 All 20 +100 BW 19. 5 31. 2 2 49. 3 1.60:1 2. 35:1

light-density. 6 Spray-dried granular STPP 0.48 do D 14. 7 29.4 55. 0 2.00:1 3. :1

light-density. 7 .d0 14. 7 29. 4 55. 0 2. 00:1 5. 40:1 TSPP 14. 7 29. 4 55. 9 2. 00:1 1. 41:1 9 TSP d0 D 14.7 29.4 55.9 2.00:1 1.1:1

1 S'IPPsodium tripolyphos hate. 3 'ISPPtetrasodium pyrophosphate. Z Diluted with 16% addltlona water to reduce its viscosity. 1 TSP-trisodlum orthophosphate.

TABLE 11 H of Bulk Percent 01' Percent of Percent aqueous 1% Dissolving rate density, S'PPP- SIPP sodium Percent Run No Screen analysis Percent Flowability solution (0.5% 1120 S01.) g./cc. 611 0 anhy. silicate H t) 0 1 +10 mesh 10. 5 Free-flowing. 10.5 F. 50.0., 0.67 7. .2 50.0 31. S 11.0

83. 0 140 F.30 sec.

23. 0 .do 10.5 140 F.--50 Sec. 1.10 5.3 5'5. 3 29. .1 11.5 47. 9 20. 1 9. 0

31. 0 d0 10.5 70 F. see., 0. 98 8. 7 5'3 27. 8 10.5 58. F.45 sec.

Table ll -Conlinued 4 +10 mesh 38. .do 10. 70 F.180 sec., 1. 24 3. 3 54. 0 32. 4 0. 4

14. 1 140 F.45 sec. $.13 20. 0

5. 0 ..d0 11.4 70 F.100 Sec., 0. 60 2. 0 58. 3 27. 8 13. 6 39. 0 140 F.30 sec. 56. O 0

22.0 .....d() 10. 5 70 F.120 860., 0. 90 40 36. 3 68. 5 140 F.45 sec.

73. 2 .d0 10. 7 70 F.240 see, 1. 06 35 45. 6 26. 7 140 F.60 sec.

18. 2 d0 10.5 70 12-240 sec., 0.92 28. 5 72. 7 140 F.60 sec.

31. 6 .-d0 11. 3 70 F.--165 sec., 0.96 5- 66. 8 140 F.50 Sec.

STPP-GH;O-hexahydrated sodium tripolyphosphate. b S'IPP anhy.-anhydrous sodium tripolyphosphate. Free moisturenot mglegularlv hound What is claimed is: 1. Process of producing strong, free-flowing, completely soluble, dry, granular particles containing as essential ingredients a mixture of a hydratable alkali metal phosphate and an alkali metal silicate wherein the SiO to said phosphate mole ratio is at least 1:1, comprising heating said alkali metal phosphate in particulate form to a temperature of about 60 to about l00 C., gradually adding an aqueous, alkali metal silicate solution having an SiO /M O weight ratio of about 2.00:1 or below to said phosphate, wherein M is selected from the group consisting of sodium and potassium, maintaining the resulting mixture of said alkali metal phosphate and said silicate solution at a temperature of about 60 to about 100 C., continually evaporating water from said mixture, controlling the rate of addition of said aqueous, alkali metal silicate solud 69.5% TSPP (calculated as anhydrous tetrasodium pyrophosphate). 52.3% TSP (calculated as anhydrous trisodiuni orthophosphate.

tion to said mixture so that said mixture is maintained in particulate, dry, granular form, continuing to add said aqueous, alkali metal silicate solution until the dry, granular particles have an Si0 to said phosphate mole ratio of at least 121 and ;recovering dry, granular particles which yield a pH of at least 10.5 in an aqueous 1 percent solution.

2. Process of claim 1 wherein said temperature of said resulting mixture is maintained between about 60 to about 70 C.

3. Process of claim 1 wherein said phosphate is sodium tripolyphosphate.

4. Process of claim 1 wherein said phosphate is tetrasodium pyrophosphate.

5. Process of claim 1 wherein said phosphate is trisodium orthophosphate.

6. Process of claim 1 wherein said aqueous, alkali metal silicate solution has an SiO /Na- O weight ratio of about 2.00:! or below.

i 7. Process of claim 1 wherein the viscosity of said alkali metal silicate solution is reduced by adding water thereto.

8. Process of claim 1 wherein said dry-appearing, granular particles have a size of about l0 to mesh. 

2. Process of claim 1 wherein said temperature of said resulting mixture is maintained between about 60* to about 70* C.
 3. Process of claim 1 wherein said phosphate is sodium tripolyphosphate.
 4. Process of claim 1 wherein said phosphate is tetrasodium pyrophosphate.
 5. Process of claim 1 wherein said phosphate is trisodium orthophosphate.
 6. Process of claim 1 wherein said aqueous, alkali metal silicate solution has an SiO2/Na2O weight ratio of about 2.00:1 or below.
 7. Process of claim 1 wherein the viscosity of said alkali metal silicate solution is reduced by adding water thereto.
 8. Process of claim 1 wherein said dry-appearing, granular particles have a size of about -10 to +80 mesh. 